Recently, compactness, power reduction and high-speed drive have been eagerly demanded for equipments with a piezoelectric material including micro-pumps, micro-speakers, micro-switches and ink jet heads. In order to satisfy such demands, a piezoelectric material is formed of a thin film whose volume can be reduced as compared to the case of a conventionally greater used sintered body. Research and development for improving the piezoelectric characteristic of the piezoelectric material formed of such a thin film have been eagerly carried out. For example, Japanese Patent Application Laid-Open (JP-A) No. 2000-299510 discloses that a compositional molar ratio of Pb, Zr and Ti in a piezoelectric material with a perovskite type crystal structure containing Pb, Zr and Ti as the main components (lead zirconate titanate (PZT)), i.e., Pb/(Zr+Ti) is more than 1 and not more than 1.3, which indicates that Pb is contained excessively. Further, in accordance with the aforementioned JP-A No. 2000-299510, the thin-film shaped piezoelectric material can be easily manufactured by being formed on a substrate made of MgO, Si or the like by a sputtering method. The composition of a target used with the sputtering is a mixture of PZT and PbO, and a compositional molar ratio of PZT and PbO, i.e., PbO/(PZT+PbO) is 0.05 to 0.35. As a result, a piezoelectric material containing excess Pb can be easily obtained. This piezoelectric material has a perovskite type crystal structure that is represented by a formula ABO3 and the main component for the A site is Pb and the main components for the B site are Zr and Ti.
However, because the above-described piezoelectric material containing excess Pb may be degenerated under high humidity, it needs to be further improved. As shown in FIG. 8, a piezoelectric element is manufactured by successively forming, on a substrate 101, a first electrode 102, a piezoelectric material 103 and a second electrode 104 by a sputtering method and the like. In the piezoelectric material 103, lattice defects such as grain boundaries 103a usually exist between perovskite type columnar crystal grains. When Pb is provided excessively, the excess Pb atoms enter, as lead oxide (PbOx) and the like, the grain boundary 103a and the like. For this reason, while such a piezoelectric material 103 being exposed to high humidity (especially, high temperature and high humidity) atmosphere, when a voltage is applied between the first and second electrodes 102, 104 so as to apply an electric field to the piezoelectric material 103, a leak current is generated and thus the piezoelectric material 103 may be degenerated with high possibility.
The present invention was developed in view of such points and an object of the present invention is to obtain a piezoelectric material with a large piezoelectric constant and high reliability that is not degenerated even if being exposed to high temperature and high humidity atmosphere.